A variety of communication networks currently exist, making use of different infrastructures and different protocols or transmission technologies for exchanging data with each other. Examples of such communication networks include Local Area Networks (LAN) and Wireless Local Area Networks (WLAN), both of which allow the interconnection of communication devices e.g. computers, which are arranged in a communication network, on the basis of the Internet Protocol (IP). In the field of telecommunications, communication networks include communication devices which function in accordance with the GSM standard (Group Special Mobile) and communication device which function in accordance with the DECT (Digital Enhanced Cordless Telecommunication) or UMTS (Universal Mobile Telecommunications System) standards.
In the following, any reference to a communication device is understood to include both mobile devices and devices which function with the aid of line-based technologies. The communication devices which are assigned to a communication network are also referred to as computers or subscriber devices in the following. While the term ‘computer’ represents an unspecified communication device, the term ‘subscriber device’ represents a specific communication device, e.g. a communication device which is assigned to a user.